A swing state - by definition - should be a state that has actually voted for both parties in recent history.
A state that is consistently close - but nevertheless hasn't actually voted for both parties anytime recently - may be a competitive state, but is not a swing state. Prior to 2016, the perfect examples of competitive states would have been Wisconsin and Pennsylvania; Ohio and Florida the perfect examples of swing states.
Personally, I consider the definition of "swing state" to be a state that has voted for both parties at least once in the past three elections. While this definition isn't perfect (see: IN), it is more often than not a better one than people conflating "swing state" with "competitive state".
One must note that this approach basically created the whole notion of the Blue Wall to the point that even affected decision making within the Clinton camp though (not going to WI). "Yet its competitive, but it will never flip because it is not a true swing state, they haven't won it since 1984".
